Acid Base
Heather Wacholz
TCCC
Acid-Base Balance (pH)
Acid—substance containing
hydrogen ions that can be
liberated or released
Base—substance that can trap
hydrogen ions
Homeostasis
Major Homeostatic Regulators of Hydrogen
Ions
Buffer systems
Carbonic acid–sodium bicarbonate
Phosphate
Protein
Respiratory mechanisms
Renal mechanisms
Hydrogen Ion Balance
Homeostatic Mechanism
 Plasma pH is an indicator of hydrogen ion (H+) concentration
 Measures the acidity or alkalinity of the blood
 Homeostatic mechanism keep pH within normal range (7.35-7.45)
 The buffer system is the kidneys and lungs
 The H+ is extremely important
 The greater the concentration the more acidic the solution therefore the
lower the pH and the less the concentration the higher the pH and the
more alkaline.
Normal values
Arterial Blood
pH
7.35
7.45
Normal PCO2
Arterial Blood
PCO2
35
45
mmHg
mmHg
Normal PO2
Arterial Blood
PO2
80
mmHg
100
mmHg
Normal PO2
Arterial Blood
HCO3-
22
mEq/L
26
mEq/L
The Kidney and Lung Help Regulate pH
Role of Lungs
 The lungs control the CO2
 The lungs control the carbonic acid of the extracellular
fluid (ECF)
 This works by adjusting the ventilation in response to the
level of CO2 in the blood
 For example: A patient with a PCO2 80 mmHg (Arterial
Blood Gas) may breathe 40 breaths per minute to
remove the high CO2.
Role of the Kidney
 The kidneys regulate the bicarbonate level in the ECF
 The kidney can regenerate or reabsorb bicarbonate
 During respiratory acidosis and most cases of metabolic acidosis the
kidneys excrete H+ ions and conserve HCO3- to help restore balance
 During respiratory alkalosis and metabolic alkalosis the kidneys hold onto H+
ions and excrete HCO3 If the patient is in renal failure the kidneys can not compensate for acidosis
Acid-Base Imbalances
 Occur when carbonic acid or bicarbonate levels become
disproportionate
 Respiratory acidosis—primary excess of carbonic acid in ECF
 Respiratory alkalosis—primary deficit of carbonic acid in ECF
 Metabolic acidosis—proportionate deficit of bicarbonate in ECF
 Metabolic alkalosis—primary excess of bicarbonate in ECF
Tests for Monitoring Acidosis and
Alkalosis
Monitor with Arterial blood gas (ABG)
Monitor with Venous blood gas (VBG)
Monitor with Capillary blood gas
(CBG)
Causes of Metabolic Acidosis and
Manifestations
Direct loss of HCO3Diarrhea, diuretic use, early renal
insufficiency, excessive administration of
chloride,
Headache, confusion, drowsiness,
increased respiratory rate, nausea, and
vomiting
Example ABG Displaying Metabolic
Acidosis
Treatment of Metabolic Acidosis
 Correcting the imbalance
 Bicarbonate is administered
 Eliminating chloride
 With the reversal of acidosis the patient may go from hyperkalemia to
hypokalemia (the K+ moves back into the cell as the acidosis corrects)
 Example the diabetic ketoacidosis patient.
 Monitor serum K+ level closely
 With chronic metabolic acidosis treat calcium level first
Causes of Metabolic Alkalosis and
Manifestations
 A common cause is gastric suctioning, vomiting, pyloric stenosis, diuretics
that promote the excretion of potassium, excessive antacid abuse, and
ACTH excretion
 The kidneys conserve K+ and H+ excretion increases; K+ leaves the cell and
H+ enters to try and maintain balance
 Symptoms of decreased Ca+ ionization, tingling of fingers and toes,
dizziness, hypertonic muscles
 Sometimes decreased respirations
 Tachycardia
 Symptoms of chronic the same as acute
Example of ABG Metabolic Alkalosis
Causes of Respiratory Acidosis and
Manifestations
 Inadequate secretion of CO2
 This can cause a decrease in oxygen levels too
 Symptoms include elevated HR, RR, elevated BP, and VF
 Confusion
 Increased ICP
 Patient's with chronic COPD may not develop symptom
of high CO2 because of compensated renal changes
Example of Respiratory Acidosis
Treatment of Respiratory Acidosis
Improve ventilation
Bronchodilators and antibiotics
Blood thinners if cause of acidosis PE
Mechanical ventilation (Intubate patient)
Decrease CO2 slowly because the kidneys can
not excrete Bicarbonate too quickly
Treatment the same for chronic
Causes of Respiratory Alkalosis and
Manifestations
 Hyperventilation
 Extreme anxiety, hypoxemia, early stage of ASA overdose
 Gram negative bacteria, inappropriate ventilator settings
 Symptoms include lightheadedness, numbness and tingling of
fingers and toes
 Decreased ability to concentrate
 Loss of consciousness
 Tachycardia
Example ABG of Respiratory Alkalosis
Treatment for Respiratory Alkalosis
Monitor electrolytes
Treat the underlying cause
Instruct the patient to breath slower; give
the patient a paper bag to breath in
 If the cause is anxiety get an order for
Xanax or Ativan
When You Think of CO2
•Monitor
pH
LUNGS
CO2
•Look at CO2
When you Think of Bicarbonate
•Monitor
pH
Kidneys
HC03-
•Look at HC03-
Alkalosis and Acidosis
Five Step Approach
 1) First note the pH is it normal, high, or low
 2) Next note the primary cause of problem. This is done by evaluating the
PaC02 and HCO3- in relation to pH
 3) Next look at compensation
 4) This means if the patient has both respiratory and metabolic alkalosis or
acidosis
 5) If metabolic acidosis occurs calculate anion gap (AG) to determine the
cause
What is AG?
 This test looks at electrically charged particles in your blood to help your
doctor diagnose acid-base imbalances. The test results are calculated
from the results of an electrolyte panel, another blood test.
 The value for the anion gap tells your doctor something about which
charged particles besides sodium, chloride, and bicarbonate ions must be
in your blood to make it neutral.
 This test gives clues about different types of acidosis, when your blood is too
acidic; and alkalosis, when your blood is not acidic enough. Acidosis in
particular can be life-threatening, so it's important to find the cause and
treat it as soon as possible
Calculating AG
 AG = Na – (CL + HC03- )
 Normal AG = 10 to14 mmol/L
 For example patient Na = 140, CL = 105 and HC03- = 25
 AG = 140 – (105 + 25) = 10 so this would be a normal AG
References
 Hinkle, J. L., & Cheever, K. H. (2014). Brunner & Suddarth's textbook of
medical-surgical nursing. Bethlehem, Pennsylvania: Wolters
Kluwer/Lippincott Williams & Wilkins.
 University of Rochester Medical Center. (2015, January 19). Retrieved from
http://www.urmc.rochester.edu/encyclopedia/content.aspx?ContentTypeI
D=167&ContentID=anion_gap_blood